Cellulose ethers have been used widely in the paint industry as thickeners for emulsion paints. Although these products like hydroxyethyl cellulose, methylcellulose derivatives, ethylhydroxyethyl cellulose and carboxymethyl-cellulose provide the paints with a number of good paint properties, these materials demonstrate shortcomings in the area of rheology. The quality of paints has constantly improved over the last decade with the demand for improving flow, film build, and spatter resistance also increasing.
Associative cellulose ethers were developed to meet this increase in demand for paints with better performance properties. Associative thickeners like hydrophobically modified ethoxylated urethanes (HEURS) were not able to be used as single thickener in medium to high pigmented latex paints because the amount of binder present in these paints is relatively low. Associative thickeners like hydrophobically modified hydroxyethylcellulose (HMHEC) were developed by Aqualon Company, a division of Hercules Incorporated, for use primarily in the paint industry. These HMHEC products are marketed commercially under the trademark Natrosol Plus.RTM. and perform extremely well as compared to those prepared with other well known cellulosic polymers for improving flow, film build, and spatter resistance in paints. These Natrosol Plus products, on the other hand, thickens the paint by dual mechanism, i.e., water phase thickening and network formation through hydrophobic interactions, and can, therefore, be used as a single thickener. These Natrosol Plus.RTM. products are hydrophobically modified cellulose ether derivatives modified with long chain alkyl groups described by Landoll in U.S. Pat. No. 4,228,277 and 4,352,916. Other patents that describe different hydrophobically modified cellulose ethers useful in paints are U.S. Pat. No. 4,902,733 (Angerer) and U.S. Pat. No. 5,124,445 and 5,120,838 (Just et al). Notwithstanding, this product's major use is in medium to high pigmented paints (i.e., paints with a pigment volume concentration (PVC) of greater than 40%).
The marketplace is still demanding a new generation of products with increased thickening efficiency and film build properties. The instant invention addresses this need by introducing an additional thickening mechanism to the thickening efficiency of Natrosol Plus products; it has been found that ionically modified hydrophobically modified hydroxyethyl cellulose ethers using a quaternary nitrogen-containing cationic moiety can improve the efficiency of all waterborne paints.
Water-soluble quaternary nitrogen-containing cellulose ethers have been described in U.S. Pat. No. 3,472,840 (Stone et al) that are useful in a variety of applications. U.S. Pat. No. 4,663,159 also describes a water-soluble, cationic polysaccharide, including quaternary nitrogen-containing cellulose ethers, containing a hydrophobic substitution that provide aqueous solutions having enhanced viscosity, foaming and preferably improved surface properties; these cationic polysaccharides are useful in personal care, emulsion, and cleanser products.